Pwll Y Rhyd Extensions

This article first appeared in Newsletter 1987 No. 1 produced by Unit Two Cave Research & Exploration and is reproduced with permission.

Graham Christian

Pwll y Rhyd, Ystradfellte, Powys
NCR SN 9113 1379
Elevation 289m AOD Length of extensions 380m
Map OS 1:10,000 SN91SW



Whilst walking one day in the area, dive Jones (SWCC) and family were keeping a look out for anything interesting. Anwen noticed a small hole in the bed of the Little Neath River, hard under the right-hand cliff about 20m upstream of the chasm of Pwll y Rhyd. Rocks were removed and a deep rift was revealed. After a few trips by Owain Jones and Jon Young, Andy Dawson, Dave Kaye and others of Croydon CC, a low entrance at the bottom of Pwll y Rhyd was opened and over 300m of passage was explored to beyond a canal to find the diving line that proved that John Parker and Martyn Farr had been there first, but via White Lady Cave and a long sump.

Description of the Cave

Opposite the sump pool in Pwll y Rhyd, under Urn north wall, is a low arch that may be blocked with shingle and rounded boulders. From here a low passage heads north, up dip, with the crawling relieved by a few cross joints in the roof. This passage may also be blocked by pebbles and sand. After about 25m there is a junction. The right fork quickly leads to a 5.8m aven to daylight, the original entrance in the river bed. To the left, a gritty slope leads up to a cross joint followed by a flat out crawl to a cross rift. To the right is an aven to 3.7m while to the left there is a squeeze under a rock arch (which sometimes needs digging out) leading to more crawling until it is possible to sit up at a junction. Straight ahead leads via a left turn to a tight, muddy descending passage, past the only major formation in the cave, to a sump pool.

Turning right at the junction leads, after more crawling and a short, steep slope, to another cross rift where it is possible to stand up again. To the right, avens reach up about 6m. To the left, a second rock arch can be climbed over but it is easier to crawl under, Particularly as the explorer will be getting used to it by now! The narrow rift ends at a right turn into yet another low crawl to a cross joint with a muddy pool to the right and a rock-strewn chamber to the left.

Ducking through the pool leads to a chamber terminated by fallen blocks that can be passed by crawling through a low bedding plane to the left, followed by turning right and squeezing back under the blocks. A steeply descending sandy slope brings one to a chamber with an aven in the roof. To the left (east) is low and sandy to a small tight passage, while straight on leads via a tight squeeze into the bottom of the cross-rift with the 8m avens previously mentioned.

From the rock-strewn chamber, a dry crawl on hands and knees leads to a boulder pile and, shortly after, becomes too tight. A wet crawl on hands and knees along a 20m canal leads to a stooping-sized passage. A hole up to the right leads into a choked phreatic passage, blocked completely to the right, but showing more open passage to the left, past a small piece of (so far) clean flowstone. Following the main passage, a junction is reached with a larger passage carrying a minute stream on the floor. Turning right, upstream leads past false floors and straws (care!) to an inlet under the left wall and a sandy mud slope up. Looking right at the top of the mud slope you will see the small flowstone formation mentioned above. To the right is a dug out squeeze that leads to a mostly filled passage that is choked completely after about 3Cm.. Retracing your steps downstream, beyond the junction, past mud banks, takes you to the sump that connects with White Lady Cave and the sump pool in Pwll y Rhyd.


The cave is basically phreatic in origin, with some vadose modification. Almost all the passage roof is rounded, the exceptions being where the passage is formed on an east-west joint and where avens have formed with some breakdown. As shown by Jon's Dig, the original phreatic system underwent a period of infilling, in common with other caves in the area. The small inlet at the top end of White Lady Passage has helped to wash out this infill, so that the full passage size can be seen. The rest of the cave is floored with varying quantities of sand, mud and round pebbles, and is periodically inundated in times of flood. It was noted on the surveying trip in October 1986 that the disturbed floor material of our August trip had been washed smooth, with the exception of the small area around the 6m avens and the mud banks at Jon's Dig. This was almost certainly the result of the floods on 25 August 1986. Further rain washed sand and gravel into the passage between the second cross rift and the first fork, barring access on a trip on 6th December. It was noted on this trip that some of the river was flowing into a bedding plane under the north wall of the Pwll y Rhyd chasm and flowing out of the entrance to the Extensions. The immediate impression was that the cave was emitting a sizeable stream, but closer investigation revealed only the merest trickle actually flowing out of the Extensions.

The orientation of the passages is clearly controlled by the two joint sets, N-S and E-W, as seen in the main system of Little Neath River Cave. The gradient of the cave is controlled by the dip of the strata which is to the south at about 4 or 5 degrees. Having surveyed Martyn Farr's "Inlet Series" to Grade 5 one can now see that it lines up nicely with the sump and the rest of White Lady Cave, and leaves one to speculate about an old phraetic system that ran down through Town Drain and Foot and Mouth Passage, until the River Neath cut down and threw a hydrological spanner in the works.

The Survey

This was undertaken on three trips, the first two of which were terminated when it was no longer possible to write legibly, due to the first stages of hypothermia! Having got wet early in the trips, slow progress and lying down for many legs of the survey, coupled with straining one's head back to read the instruments, or any of the other weird contortions that surveying in tight spaces necessitates, made for rapid fatigue, and therefore three trips were required to survey a relatively short piece of cave. Nevertheless, the majority of the cave has been surveyed to Grade 5c, Jon's Dig being a one man effort that is still probably higher that the Grade 3 claimed and the Grade 2 bit being compass bearings and paced. The survey was originally drawn up at 1:200. The compass and the clinometer readings were to the nearest 0.5 degrees, the tape readings were to the nearest 10cm. Passage details were measured wherever there was a significant change, although not all details are shown on the drawing. My thanks go to Peter Burgess for his half of the survey work.

Pwll Y Rhyd Extensions

Graham Christian